Presensitized printing plate and method for preparing same



Jan. 26, 1960 R. GUMBINNER 2,922,715

PRESENSITIZED PRINTING PLATE AND METHOD FOR PREPARING SAME Filed March 26, 1956 INVENTOR. #06567- ed/ul/Awae BY WW6, 2

A'rraezvryw PRnsENsrrIzEo PRINTING PLATE AND METHOD FOR PREPARING SAME Robert Gumbinner, Tarrytown, N.Y., assignor to Polychrome Corporation, Yonkers, N.Y., a corporation of New York Application March 26, 1956, Serial No. 574,037

6 Claims. (Cl. 96-33) My invention relates to a new and improved presensitized planographic printing plate and a new and improved method of making such a plate.

The art of planographic printing depends upon the immiscibility of grease and water and upon the preferential retention of a greasy image-forming substance by the image areas, and a similar retention of an aqueous dampening fluid by the non-image areas. When a greasy image is imprinted upon a suitable surface, and the entire 'light sensitive coating is exposed to light through a negative, and the image portion of the plate becomes vhardened and made insoluble in water by the action of the light. The unexposed light-sensitive coating is then removed by a de-sensitizing solution leaving a waterreceptive undercoating as the non-image area.

It has been known to use, as the base material in a pre-sensitized plate, either a waterproofed paper or a flexible sheet of metal. Typical metals which may be usedare aluminum, steel, zinc, magnesium, chromium and copper.

Because paper is relatively coarse-grained and has a tendency to stretch, a plate having a metallic base will givefiner reproduction and longer service than will a paper-base plate. When it is desired to coat a metallic plate with a light-sensitive material, however, it is neces- :sary to'provide the metal with a surface to which the material may adhere, since it will not adhere to the bare metal. This may be accomplished by coating the metal with a hard siliceous layer applied by treatment with an alkali silicate. water-receptive under coating for the light-sensitive material.. The present invention relates to this type of plate, and constitutes an improvement over the embodiments shown in co-pending applications now United States Patents Nos. 2,882,153 and 2,882,154 which are owned by applicants assignee.

More particularly the present invention is concerned with the problem of hardening the silicate coating on the metallic base with a substance which will not attack the metal. The above co-pending applications refer to the useof calcium nitrate as the hardening agent for smooth and grained plates, respectively..

Although the use of calcium nitrate has been commercially successful, it has now been found that it is now' possible, by other means, to simultaneously harden the silicate coating and neutralize any alkali which may be present therein- This is accomplished through the treatiment ofj the silicate coating with a hardening agent This layer provides an adhesive and a- .United States Patent Upon subsequent applicacomprising an organic acid-which willnot attack the;

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, Patented Jan. 2e, 1960 metallic base and more particularly with an acid from the group consisting of citric and tartaric acids.

The acid treatment may be employed either in combination with a smooth base plate or with a grained plate. Thus in addition to providing an effective undercoating for the light sensitive substance, the use of these acids do not in any way interfere with the permanently hydrophilic properties of the silicate undercoating and its ability to tenaciously hold the light sensitive coating. This provides for a plate having longer storage life, longer press life and images of sharp detail.

In addition, when itis desired to grain the plate prior to application of the silicate coating, the plate made by the present invention will also have a tendency to be less susceptible to halation, i.e., the appearance of a large darkened area around half-tone dots when impurities such as dust particles may adhere to the surface of the plate.

Accordingly, it is an object of myinvention to provide a plate of the type comprising a metallic base, a siliceous coating therefor, and a treatment for said siliceous coating which will not attack the metallic base but which will harden the silicate and make it an effective undercoating for a light-sensitive substance.

Another object of my invention is to provide a presensitized plate having a longer storage and press life.

Still another object is to provide a plate which will be highly sensitive and provide images of sharp detail.

Yet another object is to provide a pro-sensitized plate which will provide an image relatively free fromthe effects of halation.

These and other objects of my invention will be more clearly understood from the description which follows.

Essentially, my invention concerns a plate having a metal base, the surface of which is made permanently hydrophilic by treatment with a silicate solution and the subsequent treatment of the silicated surface with an organ c acid which will harden the silicate, neutralize any alkali present therein and at the same time not attack the metallicbase.

In a more specific embodiment my invention involves the preparation of an aluminum base plate by treatment with an alkali silicate solution so as to provide thereon a thin silicate coating which will be permanently hydrophilic and to which a light sensitive coating, such as a diazo resin, will tenaciously adhere.

In c'ontradistinction to methods proposed by the prior art, after the metallic base has been treated with alkali silicate, there is no need to make such silicate surface free of water soluble material. It has in fact been found to be highly advantageous through treatment with an organic acid such as citric or tartaric acid to add to the silicated surface these water soluble acids. The acid treatment eliminatesthe necessity for the washing step and at the same time neutralizes any alkaliremaining on the silicated surfaces from the alkali silicate treatment. This is necessary because the alkali in the silicate coating will cause hardening of a light sensitive diazo layer to an ink receptive state.

It is important that the acid used will not attack aluminum or any other metal which may be used as the base for the plate. Thus, in the case of aluminum plates, the use of citric and tartaric acids is to be preferred over stronger inorganic acids as the latter will form undesirable compounds and oxides on the aluminum surface. The citric or tartaric acid merely serves to neutralize the alkali silicate without causing this undesirable action.

for use inconnection with planographic printing plates.

A typical example of such a diazo compound is the.con-

which will not attack the metallic plate.

the case of aluminum, I have found that acids from the densation product of paraformaldehyde and pafadiazo- It is also possible to use polymeric.

diphenylamine. azido resins as well as other diazos which are now well known to those skilled in the art.

The metallic base which is preferably aluminum is prepared for the silicate treatment either by etching the same with acid and alkali or by graining. If a smooth plate is desirable, the metal is treated with phosphoric or sulphuric acid so as to give it a sufficient tooth to hold a siliceous coating. Because of easier handling and the fact that lower temperatures may be used, phosphoric acid is preferred for this treatment.

Ordinarily a solution by volume of 85% phosphoric acid is adequate although a solution would be preferable. Of course the concentration may be higher if desired. The acid treatment is carried out between 80 C. and 100 C. and preferably between 90 C. and 95 C. If the temperatureis too low, the treatment is ineffective and the siliceous coating cannot be held to the metallic surface, and if too high, the etching is not fine enough. The length of time for the acid treatment is usually between 1 and 1 minutes, but is not critical since it may vary with the temperature and concentration of the acid solution as well as with the particular grade of aluminum which is to be etched.

If instead of the above, a grained plate is desired, the graining may be performed by any of the mechanical means well known in the art, e.g., by rubbing with an abrasive, sandblasting, or wire brushing. Sandblasting is preferable since it is more easily controlled to dent rather than out into the. surface of the metal.

In sandblasting the aluminum or, other metal, the sand is forced through a nozzle under. high compression for a length of time such that the surface is completely grained. This can be easily determined .by visual examination, preferably with the use of a magnifyingglass. The metallic surface should have the. appearance of being dented rather than abraded. Obviously, the type and coarseness of the sand maybe varied depending on the type of metal and the degree of roughness desired in from to 30 seconds to remove the alkaline residue, 7

after which the impurities are removed from the surface by a desmutting process. Typical desmutting solutions are either 50% nitric acid or a mixture of 3% chromic, sulfuric and phosphoric acids. Then the plate is again rinsed and a siliceous layer is formed bydipping the plate in a. sodium silicate solution at elevated temperatures, preferably above 85 C.

This is followed by the novel step ofhardening'the siliceous layer by treating the plate withan organic acid Specifically in treatment is usually performed between 15 and 50 0,

preferably at room temperature. I

If desired, after this acid treatment, the plate. may

.then'be immersed in the. silicate bath and the hardening treatment repeated. This may be desirable because two thin coatings of silicate will tend to give a longer and cleaner running plate than would be, attained with a single thicker layer, sincea. thick siljcatelayer-does not allow .assmugh penetration of the acid,- neutralizerqhardener.

After the second silicate coating, a further acid treat? ment is necessary in order. for the plate. to stlflady 9 contact with the light sensitive diazo material. There are numerous diazo compounds which may be used and which, prior to the present invention, have been found to be sufficiently light hardenable to be useful in pianographic printing processes.

A typical compound as previously, mentioned, is the condensation product of paraformaldehyde and paradiazodiphenylamine. The sensitizer may comprise 1 percent diazo and 0.1.percent of'a 10v percentsolution of saponin. In using the light sensitive diazo resins,fit is also possible to provide an anti-oxidant in the form of hydroquinone which would be added to the hardened silicate layer prior to diazo treatment. The hydroquinone may be applied as, a .01 to 0.1 percent aqueous solution.

Following is a specific example of a method of preparing an improved aluminum plate which is treated with an alkali silicate, the silicate layer being subsequently hardened and neutralized with. citric acid.

Example I An aluminum plate, ten inches by fifteen inches and .0055 inch thick, was treated at 90 C. for one and a half minutes with a ten percent solution of eighty-five percent phosphoric acid. The plate was then rinsed in water at room temperature and immersed in an alkaline solution of .6 percent of sodium hydroxide, 1.2 percent of tetrasodium pyrophosphate, and 1.2 percent of. sodium tripolyphosphate, for one minute at 55 C. The alkaline residue was then removed by a rinsing for thirty seconds in water at room temperature and then in a desmutting solution of three percent by weight of-Cro three percent by volume of H andthree percent? by volume of H PO Then it was rinsed for three minutes in running water and immersed in a silica bath consisting of (Na O:SiO =1:3.22). This solution was maintained at C. It was then hardened by immersionin a 25" percent solution of citric acid at 25 C. for two minutes. After the citric acid treatment, it was treated with a .05 percent aqueous solution of hydroquinone. Then the plate was coated with an aqueous solution of 1 percent diazo and 0.1 percent of a 10 percent solution of saponin. The diazo used was the condensation prodnot of paraformaldehyde and paradiazodiphenylamine (four parts of formaldehyde to thirty parts of paradiazodiphenylamine by weight). The plate was coated on both sides, retaining about 0.25 cc. of diazo solution per side. After drying, the plate was ready for use.-

Example II The procedure of Example Iwas repeated, substitut-" ,oughly grained metallic surface.

It is to be understood, that my process is not limited to the specific example herein described, but is to'include the many variations thereof which would beobvious to those skilled in the art.' Therefore, although I have described preferred forms of my'inventioml do not wish to be limited except assetforth inthe appended claims.

Lclaim;

1 .v The method cit-preparing.apmscnsitized metallic base rinting. plate comprisingv treatmethe metallic .S'urface with an alkali silicate so as to form a hydrophilic siliceous layer thereon, neutralizing any alkali in the siliceous layer and hardening the same by treatment with a water-soluble organic acid from the group consisting of citric and tartaric acids and subsequently coating the treated siliceous layer with a light-sensitive diazo compound.

2. A metallic base printing plate made in accordance with the method of claim 1.

3. The method of preparing a presensitized aluminum base printing plate comprising treating the aluminum surface with an alkali silicate so as to form a hydrophilic siliceous layer thereon, neutralizing any alkali in the siliceous layer and hardening the same by treatment with an 0.1 percent to 50 percent solution of a watersoluble organic acid from the group consisting of citric and tartaric acid at a temperature in the range of 15 C. to 50 C., and subsequently coating the treated siliceous layer with a light-sensitive diazo compound.

6. The method of preparing a presensitized aluminum base printing plate comprising treating the aluminum surface with an alkali silicate so as to form a hydrophilic thin siliceous layer thereon, neutralizing any alkali in the siliceous layer and hardening the same by treatment with a 1 percent to 50 percent solution of a watersoluble organic acid from the group consisting of citric and tartaric acid at a temperature in the range of 15 C. to 50 C. and then treating the acidified siliceous. layer with a 0.01 to 0.1 percent aqueous solution of hydroquinone anti-oxidant and subsequently coating the treated siliceous layer with a light sensitive diazo compound.

References Cited in the file of this patent UNITED STATES PATENTS 2,100,063 Zahn Nov. 23, 1937 2,532,866 Toland et al. Dec. 5. 1950 2,560,137 Slifkin July 10, 1951 2,691,584 Smith et al. Oct. 12, 1954 2,714,066 Jewett et al. July 26, 1955 2,760,431 Beatty Aug. 28, 1956 

1. THE METHOD OF PREPARING A PRESENSITIZED METALLIC BASE PRINTING PLATE COMPRISING TREATING THE METALLIC SURFACE WITH AN ALKALI SILICATE SO AS TO FORM A HYDROPHILIC SILICEOUS LAYER THEREON, NEUTRALIZING ANY ALKALI IN THE SILICEOUS LAYER AND HARDENING THE SAME BY TREATMENT WITH A WATER-SOLUBLE ORGANIC ACID FROM THE GROUP CONSISTING OF CITRIC AND TARTARIC ACIDS AND SUBSEQUENTLY COATING THE TREATED SILICEOUS LAYER WITH A LIGHT-SENSITIVE DIAZO COMPOUND. 